The aim of this project is to identify and characterize the gene or genes responsible for the Alagille syndrome. Elucidation of the genetic basis of the syndrome will necessarily include gene identification followed by studies of gene regulation, products(s) and function(s). It is likely that an understanding of the molecular events that give rise to the hepatic abnormalities in Alagille syndrome will also provide new insight into other hepatic and biliary disorders. The Alagille syndrome, which has a complex phenotype and inheritance pattern, has been localized to a small region of chromosome 20. The Alagille Syndrome is a clinically defined disorder characterized by cholestatic liver disease, a peculiar facies, structural heart defects, vertebral anomalies and ocular abnormalities. The association between Alagille syndrome and chromosome 20p was first noted in a case report describing a patient with del(20)p11.23-pter and a phenotype consistent with the Alagille syndrome. Despite the identification of the Alagille region, molecular characterization of the gene or genes causing the syndrome has not been achieved. In order to identify the causative gene(s), cytogenetic and molecular screening of large numbers of patients for deletions in the Alagille region will be performed. Once the region is more narrowly defined, candidate genes within the area will be selected for further study. Selection of genes will be accomplished by three methods. First, known markers will be mapped to chromosomal breakpoints and/or within deletions and those markers then will be used to select genomic and cDNA clones. Second, candidates will be selected from gene families with known functions that would be predicted to affect the organ systems with phenotypic abnormalities in the Alagille syndrome. Lastly, subtractive screening methodologies will be used to select sequences with altered expression in an affected liver sample. Once isolated, these candidate genes will be characterized by Northern blot analysis to determine the pattern of tissue expression in adult and fetal tissues. Southern blot analysis will be used to determine the incidence of hemizygosity, and single strand conformational polymorphism screening will be used to identify mutations.